1. Field of the Invention
This invention relates to a hydrogenation catalyst and a hydrogenation process wherein said catalyst is used. More particularly, this invention relates to a hydrogenation catalyst and to a process wherein said catalyst is used to hydrogenate ethylenic and/or aromatic unsaturation.
2. Prior Art
Catalyst for hydrogenating chemical compounds containing ethylenic and/or aromatic unsaturation, are, of course, well known in the prior art. Useful catalysts include such heterogeneous catalysts as nickel on kieselguhr, Raney nickel, copper chromate, molybdenum sulfide, finely divided platinum, finely divided palladium, platinum oxide, copper chromium oxide and the like, as taught, for example, in U.S. Pat. No. 3,333,024. Useful catalysts also include homogeneous systems such as those prepared with rhodium compounds or complexes, as taught, for example, in U.K. Patent No. 1,558,491 and in U.S. Pat. Nos. 4,581,417 and 4,674,627 and those prepared with ruthenium complexes as taught, for example, in U.S. Pat. No. 4,631,315. As is known in the prior art, certain of these catalysts are quite effective in the hydrogenation of ethylenic unsaturation but many of these catalysts are not particularly selective as between ethylenic and aromatic unsaturation and therefore cannot be effectively used to selectively hydrogenate ethylenic unsaturation in a compound containing both ethylenic and aromatic unsaturation. Moreover, those catalysts involving the use of a rare or precious metal are not, generally, practical for large scale commercial use in processes wherein catalyst recovery is inefficient, as in polymer hydrogenation processes, due to their limited availability and relatively high costs.
Catalysts which are useful in the hydrogenation of ethylenic unsaturation, which catalyst may be used to effect selective hydrogenation as between ethylenic and aromatic unsaturation, also include catalysts which are frequently referred to as homogeneous systems prepared by combining an iron group metal compound, particularly a nickel or cobalt compound, with a reducing agent. Such catalyst may be the reaction product of an iron group metal alkoxide and an aluminum hydrocarbon compound as taught, for example, in U.S. Pat. No. 3,113,986; the reaction product of an iron group metal carboxylate, chelate or alkoxide and a lithium or magnesium hydrocarbon compound as taught, for example, in U.S. Pat. No. 3,541,064; the reaction product of a nickel or cobalt alkoxide or carboxylate and an aluminum trialkyl as taught, for example, in U.S. Pat. No. 3,700,633 or the reaction product of an iron group carboxylate, an enolate, a phenolate or a salt of certain sulfur-containing acids and half esters thereof and a metal alkyl of a metal selected from Groups I, II and III as taught for example in British Patent Specification 1,030,306. Nickel/Alkyl Aluminum hydrogenation catalysts have been improved by the addition of water in amounts from 0.4 to 1.3 moles of water per mole of nickel. As is known in the prior art, these catalysts can be used in a manner such that essentially all of any ethylenic unsaturation contained in the chemical compound is hydrogenated while essentially none of the aromatic unsaturation contained therein is hydrogenated. These catalysts, are, however, generally, far less active than the non-selective catalysts heretofore known in the prior art, and, as a result, longer holding times are frequently required to effect a high degree of selective hydrogenation. Further, most, if not all, of these selective catalysts generally result in significant conversion of ethylenic unsaturation in relatively short contacting times, thereby preventing good control over the extent of conversion of the ethylenic unsaturation when partial hydrogenation is the desired objective.
More recently, it has been discovered that better control over the rate and extent of the hydrogenation can be achieved if a catalyst prepared by combining a Group VIII metal compound with certain alumoxanes, particularly a methylalumoxane, is used, as taught in U.S. patent application Ser. No. 07/289,158, which application was filed Dec. 23, 1988 and pending concurrently herewith. As indicated in this application, the hydrogenation with catalysts prepared with methylalumoxanes proceeds, initially at least, at a slower rate while a higher degree of hydrogenation can ultimately be achieved in reasonable holding times.
In light of the deficiencies of the prior art catalysts, then, the need for a catalyst which can be prepared with more readily available metals and be used to selectively hydrogenate ethylenic unsaturation in a chemical compound containing both ethylenic and aromatic unsaturation, which catalyst also enables increased hydrogenation in reasonable holding times when compared to the selective catalyst known in the prior art and still affords better control over the extent of hydrogenation, is believed to be readily apparent.